Barack Obama speaks about the National Park Service at Yosemite national park in California.
Photograph: Joshua Roberts/Reuters

Barack Obama warned on Saturday that climate change could ravage many of America’s vaunted national parks, criticizing political opponents who “pay lip service” to areas of natural beauty while opposing efforts to reduce greenhouse gas emissions.

During a visit to Yosemite national park, Obama said climate change was “no longer a threat, it’s a reality”. The first sitting president to visit Yosemite since John F Kennedy in 1962 said the famed glacial valley was already experiencing changes due to rising temperatures.

“Here in Yosemite, meadows are drying up, bird ranges are shifting farther northward, mammals are being forced further upslope,” Obama said. “Yosemite’s famous glacier, once a mile wide, is almost gone. We are also facing longer, more expensive wildfire seasons.

“Rising temperatures could mean no more glaciers in Glacier national park, no more Joshua trees in Joshua Tree national park. Rising seas can destroy vital ecosystems in the Everglades and at some point could even threaten icons like the Statue of Liberty and Ellis Island. That’s not the America I want to pass on to the next generation.”

According to the National Parks Service, which marks its centenary in August, many fragile ecosystems are “in danger of disappearing forever”. The service said glaciers could be completely gone from Glacier national park by 2020, park facilities in Alaska are sinking due to thawing permafrost and archaeological sites are under threat from sea level rise.

Obama said America’s protected landscapes are “the envy of the world”. But the president also hit out at the climate change position of presumptive Republican nominee Donald Trump, who has said he is in favour of clean air but has vowed to pull the US out of the Paris climate accord and has disparaged mainstream climate science as a “hoax invented by the Chinese”.

Obama said: “We can’t treat it like it’s someone else’s problem, it shouldn’t lead to careless suggestions that we don’t get serious about carbon emissions or that we scrap an international treaty that we spent years putting together to deal with this.

“This park belongs to all of us, this planet belongs to all of us. It’s the only one we’ve got. We can’t pay lip service to that notion and then oppose the things required to protect it. We’ve got to do a lot more. There is such a thing as being too late.”

Obama’s visit to Yosemite via helicopter caused major congestion in a park already heaving with summer visitors. Yosemite advised people to enter the park either before 8am or after 6pm to avoid the worst of the disruption. All parking, trails and climbing routes in the Lower Yosemite Falls area were shut down to allow Obama, wife Michelle and daughters Sasha and Malia to do some hiking.

The trip was greeted mostly with excitement by visitors, however, several holding up signs welcoming the Obamas and one person even pinning an invite on a bulletin board to the first family to enjoy s’mores by the campfire.

Barack and Michelle Obama take a photograph with children. Photograph: Jacquelyn Martin/AP

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French tourist Pauline Richard said: “It’s quite a good surprise. We are pretty excited. He’s quite popular [in France]. I would say he’s more popular than our president.”

Yosemite has reported visitor numbers that are 20% up on last year’s record total, amid an effort by the federal government to get more people into national parks. Fourth-graders are now given free passes but Obama said more needed to be done to connect Americans to the natural world.

“We’ve got kids all across the country who never see a park,” he said. “There are kids who live miles from here who never see this. We’ve got to change that.

“I remember being an 11-year-old kid, I remember the first time I saw a moose in a lake. The first time I saw a bear and her cub. That changes you, you’re not the same after that.”

Obama also mentioned that his administration has protected 265m acres of land – more than any other presidency. The unilateral declaration of national monuments has generally proved popular among the public but is controversial with some Republicans, who claim that more land needs to be opened up for mining and agriculture, rather than economic development through outdoor pursuits.